Remove that ugly lunar surface state! It's bad!

Fresh start -- we'll have a MainGameState with a World. Chunks!
Add world.py, forgot this...
first pass at a chunk implementation
Change camera.x and camera.y to camera.pos
Added loading and unloading of surrounding chunks
Add saving/loading of chunk textures
Implemented a carvable landscape! Whoa!
.gitignore: add *.pyo
Added worldgenstate, fixed chunk carving
Add chunk saving and loading
Implement world blitting
Added player animations! YAY
Added camera tracking
Scale down the physics

... this was way more difficult to do than it should have been
Fix world blitting
minor tweaks to moon color
Added surface generation
Remove outlines from the lunar surface background